Angiotensin II Potentiates the Slow Component of Delayed Rectifier K⁺Current via the AT₁Receptor in Guinea Pig Atrial Myocytes

BACKGROUND: Angiotensin II (Ang II) has diverse actions on cardiac electrical activity. Little information is available, however, regarding immediate electrophysiological effects of Ang II on cardiac repolarization. METHODS AND RESULTS: The present study investigated the immediate effects of Ang II on the slow component of delayed rectifier K+ current (IKs) and action potentials in guinea pig atrial myocytes using the whole-cell patch-clamp technique. Bath application of Ang II increased the amplitude of IKs (EC50, 6.16 nmol/L) concentration dependently. The stable analogue Sar1-Ang II was also effective at increasing IKs. The voltage dependence of IKs activation and the kinetics of deactivation were not significantly affected by these agonists. The enhancement of IKs was blocked by the Ang II type 1 (AT1) receptor antagonist valsartan (1 micromol/L) and was markedly attenuated by inclusion of GDPbetaS (2 mmol/L) in the pipette, indicating an involvement of G protein-coupled AT(1) receptor. The stimulatory effect was also significantly reduced by the phospholipase C inhibitor compound 48/80 (100 micromol/L) and the protein kinase C inhibitors bisindolylmaleimide I (200 nmol/L) and H-7 (10 micromol/L), suggesting that AT1 receptor acts through phospholipase C-protein kinase C signaling cascade to potentiate I(Ks). As expected from its stimulatory action on IKs, Sar1-Ang II markedly shortened the action potential duration, which could be reversed by valsartan. CONCLUSIONS: The potentiation of IKs via AT1 stimulation in atrial myocytes, accompanied by a shortening of the action potential duration, suggests a potential mechanism by which elevated levels of Ang II may promote atrial fibrillation in heart failure and warrants further investigation.